Updates of the 6S Radiative Transfer Model: A Case Study of 6S+Prosail

This study rewrites the widely used 6S radiative transfer model (RTM) in Fortran 90, to make which easily studied and used. Three surface reflectance models are also incorporated, including the PROSAIL-D canopy reflectance model, the ACRM canopy reflectance model, and the asymptotic radiative transfer (ART) snow reflectance model. The 6S+PROSAIL model is then further analyzed: (1) Sensitivity analysis (SA) of parameters of the 6S+PROSAIL model is conducted at 400-2500 nm, and SA of parameters of PROSAIL is also given. (2) Bidirectional reflectance factors of the PROSAIL and 6S+PROSAIL models are simulated over 2π space, to show their anisotropy characteristics. The analysis results provide reference information for those who intend to use these models in their applications, such as parameter inversion and observation simulation; and the updated code is helpful to users of 6S, and those who plan to put 6S and PROSAIL together.